The invention relates to receptors that bind toxins from Bacillus thuringiensis and thus to pesticides and pest resistance. More particularly, the invention concerns recombinantly produced receptors that bind BT toxin and to their use in assays for improved pesticides, as well as in mediation of cell and tissue destruction, dissociation, dispersion, cell-to-cell association, and changes in morphology.
It has long been recognized that the bacterium Bacillus thuringiensis (BT) produces bactericidal proteins that are toxic to a limited range of insects, mostly in the orders Lepidoptera, Coleoptera and Diptera. Advantage has been taken of these toxins in controlling pests, mostly by applying bacteria to plants or transforming plants themselves so that they generate the toxins by virtue of their transgenic character. The toxins themselves are glycoprotein products of the cry gene as described by Hxc3x6fte, H. et al. Microbiol Rev (1989) 53:242. It has been established that the toxins function in the brush border of the insect midgut epithelial cells as described by Gill, S. S. et al. Annu Rev Entomol (1992) 37:615. Specific binding of BT toxins to midgut brush border membrane vesicles has been reported by Hofmann, C. et al. Proc Natl Acad Sci USA (1988) 85:7844; Van Rie, J. et al. Eur J Biochem (1989) 186:239; and Van Rie, J. et al. Appl Environ Microbiol (1990) 56:1378.
Presumably, the toxins generated by BT exert their effects by some kind of interaction with receptors in the midgut. The purification of a particular receptor from Manduca sexta was reported by the present inventors in an article by Vadlamudi, R. K. et al. J Biol Chem (1993) 268:12334. In this report, the receptor protein was isolated by immunoprecipitating toxin-binding protein complexes with toxin-specific antisera and separating the complexes by SDS-PAGE followed by electroelution. However, to date, there has been no structural information concerning any insect receptor which binds BT toxin, nor have, to applicants"" knowledge, any genes encoding these receptors been recovered.
The present invention is based, in part, on the isolation and characterization of a receptor that is bound by members of the BT-toxin family of insecticidal proteins, hereinafter the BT-R1 protein. The present invention is further based on the isolation and characterization of a nucleic acid molecule that encodes the BT-toxin receptor, hereinafter BT-RBT-R1 gene. Based on these observations, the present invention provides compositions and methods for use in identifying agents that bind to the BT-RBT-R1 protein as a means for identifying insecticidal agent and for identifying other members of the BT-R1 family of proteins.